Simultaneous conditional alias creation and indexing

We store user transactions into elasticsearch. I have an req of creating an alias for each user. So whenever a user does any transaction on our site we index its transaction. But before indexing I need to check if the alias for the user already exist. And checking this takes some time. I want to know if there is any way I can simultaneously create an alias(if already not exists) and indexing the transaction at the same time.